21940681 has 16 divisors (see below), whose sum is σ = 26150400. Its totient is φ = 18392640.

The previous prime is 21940679. The next prime is 21940703. The reversal of 21940681 is 18604912.

It is a happy number.

It is not a de Polignac number, because 21940681 - 2¹ = 21940679 is a prime.

It is a super-2 number, since 2×21940681² = 962786965487522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21940601) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 15441 + ... + 16801.

It is an arithmetic number, because the mean of its divisors is an integer number (1634400).

Almost surely, 2^21940681 is an apocalyptic number.

It is an amenable number.

21940681 is a deficient number, since it is larger than the sum of its proper divisors (4209719).

21940681 is an equidigital number, since it uses as much as digits as its factorization.

21940681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1429 (or 1415 counting only the distinct ones).

The product of its (nonzero) digits is 3456, while the sum is 31.

The square root of 21940681 is about 4684.0880649279. The cubic root of 21940681 is about 279.9518667261.

The spelling of 21940681 in words is "twenty-one million, nine hundred forty thousand, six hundred eighty-one".